Overview of the New EN 60079-10-1 for ATEX Hazardous Area Classification

In industries that store, produce or use flammable gases or liquids capable of forming an explosive atmosphere, hazardous area classification is the first step required by Directive 1999/92/EC to develop the “integrated safety” process, in other words, the starting point of any risk assessment.

Both the EN 60079-10-1: Classification of areas – Explosive gas atmospheres standard and its guide UNE-EN 202007:2006 are the basic documents used to classify hazardous areas. Standards are updated periodically as technology and knowledge advance, and these changes can range from simple editorial changes to major technical changes. The latest update of the hazardous area classification standard EN 60079-10-1, from October 2016, introduces major technical changes that need to be addressed.

One of the main changes concerns the concept of “hypothetical volume of explosive atmosphere, Vz”, used in the previous version of the standard to determine the degree of ventilation. This update removes it and uses the concept of dilution instead, based on the release characteristics and the ventilation air velocity. The “hypothetical volume” concept was based on theoretical studies, while the new concepts are related to CFD (computational fluid dynamics), the computational analysis of fluid behavior.

Major technical changes have been introduced and, although it is not a harmonized standard, it is highly advisable to review calculations made with the previous standard, as differences may appear (for example, in the extent of the zones). This is a good reminder of the need to update the Explosion Protection Document (EPD) periodically, as required by Directive 1999/92/EC, which provides an opportunity to review the hazardous area classification.

Below is a summary of some of the most relevant changes in the standard:

• Several approaches to area classification have been introduced, for example using recognized international standards (such as API RP 505 and NFPA 497) or industry guides (such as IP15 or IGEM/SR/25). It also states that the calculation method and/or a combination of methods can be used.
• The different types of release (gas, liquefied gas, flammable liquid) and their behavior (buoyancy, that is, where the gas goes when it leaks) are now much better defined. Technical changes have been made to the release rate calculation:
  • An example table has been updated and expanded to determine the release hole size more accurately.
  • A discharge coefficient (Cd) has been introduced to account for viscosity and the shape of the release hole.
• The original ventilation concept has been completely changed, now including parameters such as gas dispersion and dilution in the surrounding atmosphere.
• Much more importance is given to the concept of “background concentration” in enclosed spaces. In fact, it is the main parameter that determines the resulting type of zone.
• Information has been added on the type of release (jet or diffusive) and on how ventilation works in enclosed spaces, with new formulas for calculating the ventilation flow rate (wind-driven or temperature-driven).

In addition, the new version determines the extent of classified zones with the following chart instead of formulas:

The new calculations usually result in smaller hazardous zones than before, especially outdoors. In enclosed spaces, distances are usually smaller too, but this depends heavily on whether ventilation is natural or forced and on the layout of the ventilation openings; if the resulting distances are significant, classifying the entire enclosed space is recommended.

This update also includes new area classification examples, as well as specific annexes on flammable mists, hydrogen and international standards to consider when classifying hazardous areas.

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